PHYLUM ARTHROPODA 297 



Order 5. Tanaidacea. — Malacostraca with free thoracic 

 segments except the first two, which are fused with the 

 head and extend on the sides, forming a respiratory 

 chamber. Example: Apseudes (Fig. 219). 



Order 6. Isopoda. — Malacostraca with a body generally 

 broad and flat, seven free thoracic segments, leaf-like 

 legs, and no carapace. Examples: Asellus (Fig. 220, A), 

 Armadillium, Oniscus (Fig. 220, B), Porcellio. 



Order 7. Amphipoda. — Malacostraca laterally com- 

 pressed, with elongated abdomen bearing three pairs 

 of posteriorly directed springing feet and three pairs of 

 anterior swimming feet, and without a carapace. Exam- 

 ples: Gammarus (Fig. 221, A), Talorchestia (Fig. 216), 

 Caprella (Fig. 221, B). 



Order 8. Euphausiacea. — Malacostraca with all thoracic 

 segments covered by carapace, pedunculate eyes, none 

 of thoracic limbs specialized as maxillipeds, and only 

 podobranchias present. Example: Meganyctiphanes. 



Order 9. Decapoda. — Malacostraca with first three pairs 

 of thoracic limbs specialized as maxillipeds, with five 

 pairs of thoracic walking legs, with generally all of the 

 thoracic segments covered by a carapace, and with 

 stalked, compound eyes. 

 Suborder 1. Natantia. — Decapoda with body usually 

 laterally compressed, legs generally slender, and pleopods 

 always present in full number, well developed, and used 

 for swimming. Examples: Penceus, Alpheus, Palcemonetes 

 (Fig. 224), Stenopus. 

 Suborder 2. Reptantia. — Decapoda with body not com- 

 pressed, legs strong, pleopods often reduced or absent, 

 not used for swimming. Examples: Hyas, Cancer, Cal- 

 linectes (Fig. 223), Pinnotheres, Cambarus (Fig. 202), 

 Homarus, Palinurus, Eupagurus, Gelasimus (Fig. 223, B). 



Order 10. Stomatopoda. — Malacostraca with five pairs 

 of anterior maxillipeds on the thorax, and three pairs of 



